Oligonucleotides have been proposed as potent diagnostic compounds and as new rationally designed therapeutic agents (Uhlman, 1990; Helene, et al., 1990; Helene, 1991). The mechanism of action of these compounds is based on their specific interaction with RNA or DNA regions of interest.
Several modifications of the natural phosphodiester internucleoside bond {phosphomono(Eckstein, et al., 1985; Cohen, 1993) or dithioate (Marshall, et al., 1993), methylphosphonate (Miller, 1991), phosphodiester amidate (Letsinger, et al., 1988; Froehler, et al., 1988)} have been introduced to improve (i) the stability of the oligomers in biological media, and (ii) the hybridization properties of the oligomers.
Unfortunately, the vast majority of these analogs exhibit reduced binding with target RNA or DNA strands via duplex or triplex formation (Kibler-Herzog, et al., 1991). Moreover, the presence of the stereoisomers at phosphorous in some of these analogs may complicate the binding patterns with complimentary nucleic acids (LaPlauche, et al., 1986; Bower, et al., 1987; Tidd, et al., 1988).